The basic invented breaker mechanism is an improvement of a mechanism until now used only for residential type circuit breakers. This mechanism could not be combined with the requirements for interrrupting high fault currents at high voltages (for example, 50 KA at 480 volts). It was further not available in combination with various trip units and industrial type handles.
The invention relates:
(a) The possibility to use this basic mechanism for current limiting action so obtaining industrial type high interrupting capacity circuit breakers for example 50 KA 480 volts. Such basic mechanism without the improvements is, for example, described in the book Elektrische Niederspannungs Schaltgerate by Kussy (Technischer Verlag Cram Berlin, 1969) on page 784. The mechanism has the advantage of great simplicity but in order to obtain current limiting action, the contact arms must be designed in such a way that the two arms or at least a large section of the arms be positioned parallel or nearly parallel in the closed position of the breaker with the current flowing in opposite direction in both arms, the arms having a close distance.
(b) A further improvement over the basic mechanism described by Kussy can be obtained by making the second contact arm also spring loaded so obtaining at higher fault currents an additional contact opening and increased opening speed because both contact arms are moving. The second contact arm can be under influence of a heavier spring than the first contact arm. That allows improved bouncing characteristic at the closing of the circuit breaker.
(c) The basic mechanisms described before was until now designed in such a way that the cradle was latched against a bimetal or magnet. The invented breaker latches the cradle against a lever which is pushed by a rotating teeter bar. This teeter bar is pushed by a magnet or a bimetal or a spring loaded lever operated by a magnetic latch (released permanent magnet). The rotating teeter bar is under influence of a small spring and may be used to push that armature of the magnetic latch toward the yoke of the permanent magnet by the unlatched cradle so that the circuit breaker can be later reset and latched by hand. This adaptation allows the mechanism to be used with interchangeable trip units.
(d) The contact blows open under heavy fault conditions before the breaker trips. Fast rebounding could cause welding and must be prevented. If the negative spring action and two moving contact arms do not already prevent reclosing it may be desirable to unlatch the cradle with a blown open contact arm. A further advantage of the invention is that such a current limiting circuit breaker therefore does not need an antirebound latch.
(e) The trip unit can be built in such a way that we can select trip units which trip first the one pole that carries the over current so requiring small tripping forces (adjustable magnetic trip unit or thermal trip unit) or use those which trip all poles at the same time by a cross-bar (solid state trip unit) in the trip unit.
(f) Another advantage of such a mechanism for industrial type breakers is that it can be used with an industrial type handle to secure positive action that means opening a welded contact by pushing directly the contact arm with the handle into the open position mechanically and not alone by a spring so securing that the contact arm moves to the full open position.
(g) Another advantage of the invention is that each pole is in a separate housing securing high strength, the cross-bar between poles not requiring an easily damageable cover such arrangement preventing a fault between poles due to hot gasses when interrupting high current.